The Interface Board for P1 is exactly the same as M2. It contains both the power supply circuitry and the automotive interfaces required to communicate with your car. This includes:
2x CAN bus
1x SWCAN (Single-Wire CAN)
26-pin general purpose connector
Every P1 has a 26-pin general purpose "expansion" connector that provides even more connection options. For example: UART, SPI, I2C, six general purpose 12V drivers and six 12V analog inputs. See the schematic for actual pinout details.
CAN bus is a vehicle bus standard used in most cars built after 2006. It is a message-based protocol that allows modules within a car to communicate with one another. While the physical layer is understood and open, the actual meaning of the messages sent over the bus are not. While some messages are legislated to be "standard", the majority of CAN messages in your typical car are not well documented.
The P1 has 2 CAN channels (in addition to the single-wire CAN channel) that can interface directly to the CAN bus network of your car. The P1 uses the 2 built-in CAN controllers found in the SAM3X and 2 external TJA1051 transceivers. Here is a typical example:
CAN bus connections can be found on either the 16-pin OBD2 connector on the under-the-dash P1 or the 24-pin connector used by the under-the-hood P1.
The Macchina P1 provides single-wire CAN support using a MCP2515 CAN controller.
Local Interconnect Network bus is an inexpensive, single wire, serial network protocol used in many modern cars. Typically, LIN would be used to control and monitor lower-priority devices such as seat positions, door locks, radio and illumination.
The P1 has 2 LIN channels that can interface directly to the LIN bus network of your car. Your P1 uses 2 external TJA1027 transceivers connected via UART to the processor.
Add in boot/uEnv.txt the console option to redirect output to ttyS2:
K-line (aka ISO9141, KWP2000)
ISO9141/K-line is typically found in Chrysler, European, and Asian vehicles built before around 2005. This protocol is similar to RS-232 but at different voltage levels and on a single, bidirectional line.
Some cars require a secondary line (sometimes referred to as L-Line).
P1 has two K-line channels and uses the TJA1027 transceiver to interface the 12-volt single bidirectional line from the vehicle to a 3.3V UART connection. While this part is designed for LIN, it is also K-line compatible. Here is typical interface circuit showing a channel of ISO9141/LIN connected to the UART channel of the processor.
K-line connections can be found on either the 16-pin OBD2 connector on the under-the-dash P1 or the 24-pin connector used by the under-the-hood P1.